1. Field of the Invention
The present invention relates to a solid-state image pickup apparatus, and more particularly to a solid-state image pickup apparatus configured to record, in the form of image data, raw or unprocessed data derived from light incident to a single photo-sensitive cell or pixel or a photo-sensitive cell having a plurality of photo-sensitive regions different insensitivity from each other.
Further, the present invention relates to an image recording and an image reproducing method for such a solid-state image pickup apparatus, and more particularly to a method of “RAW mode” recording image data in the form of raw data and of reproducing image data adaptively to the RAW mode recording.
2. Description of the Background Art
Today, a digital camera using a solid-state image sensor is extensively used because it has the advantage of picking up images with high picture quality and allowing the user of the camera to easily monitor images picked up. Further, an advanced digital camera is directed toward picture quality comparable with one achievable with a camera using a silver-halide photosensitive type of film. A digital camera and a camera using a silver-halide photosensitive type of film are different from each other in dynamic range available, among others. More specifically, the dynamic range of a digital camera is narrower than a dynamic range achievable with a broad latitude particular to a silver-halide photosensitive type of film. Some different schemes have heretofore been proposed to enhance the dynamic range of a digital camera, as will be described hereinafter.
U.S. Pat. No. 6,809,761 to Masaya Tamura, for example, discloses an image data forming apparatus including a range separator. The range separator divides the entire dynamic range of image signals into a first range subject to gradation conversion and a second range covering the rest so as to establish a thus adjusted complete image on a reproduction system provided with preselected lightness and tone, while preserving the compatibility of the image signals with existing image files. In this configuration, the image components or video signals, each belonging to one of the two ranges, are recorded in a recording medium together while being related to each other. This allows the image components constituting a single image in combination, but belonging to the different ranges, to be effectively used in matching relation to a display medium for reproduction, thereby accomplishing image reproduction adaptive to the dynamic ranges for displaying on monitors and reproducing prints through, e.g. photosensitive films.
Japanese patent laid-open publication No. 2001-8104 proposes abroad dynamic range, image pickup apparatus including a CCD (Charge Coupled Device) solid-state image pickup device made up of high- and low-photosensitivity cells. Signal charges output from the high- and low-sensitivity cells are converted to corresponding analog signals and then digitized by respective analog-to-digital (A/D) converters. The resulting high- and low-sensitivity video signal data are recorded in a recording medium while being related to each other. With the simple configuration, according to the above publication document, the apparatus implements correction matching with reproduction or similar post-processing to thereby provide an image with a dynamic range as broad as achievable with silver-halide photosensitive type of films. In addition, this apparatus is capable of reducing the amount of data to be written into a recording medium.
Further, U.S. patent publication No. US 2002/0057903 A1 teaches an image data recording apparatus that allows even an apparatus provided with a fixed quantization level to effectively use all data of an image picked up in a broad range. Specifically, the data recording apparatus taught in the above publication document includes a digital signal processor configured to process a video signal fed from an analog-to-digital converter through its consecutive stages. More specifically, the digital signal processor produces a difference of a signal output in each of its processing stages from a signal output just before that stage for thereby feeding eight-bit data specific to a complete image file. At the same time, the digital signal processor records parameters representative of the processing history and the difference data in a sub-file while relating them to each other, i.e. records the data in a standard file format. This allows original data of an image picked up to be fully reproduced and effectively used. The prior art disclosed in the documents thus attains a broad dynamic range for image recording so far.
There is an increasing demand for a digital camera with picture quality high enough to differentiate itself from a digital imaging function available with a modern cellular phone. While higher picture quality is achievable if the number of pixels is increased, an increase in the number of pixels results in a decrease in the photosensitive area of the individual photo-sensitive cell or image sensing device. Also, a solid-state image pickup apparatus generally has a problem that false signals including moiré appear, depending on a subject picked up.
To reduce false colors ascribable to false signals and broaden the dynamic range while promoting efficient receipt of light, U.S. Pat. Pat. No. 6,236,434 to Tetsuo Yamada discloses a solid-state image pickup device in which pixels are highly integrated to increase the quantity of incident light available. For this purpose, assuming that the distance between pixels on the same row or the same column is a pitch, then in the above apparatus pixels are shifted by half a pitch in the direction of row and/or the direction of column in a so-called honeycomb pattern. Further, the photosensitive area of the individual photo-sensitive cell includes a main region and a sub-region smaller in size than the main region, so that signal charges can be read out from the two regions either separately or at the same time.
Generally, with a digital camera available is a “RAW mode” in which entire raw data produced by a shot are recorded, in addition to a usual mode that records data in only a preselected number of pixels. The RAW mode is advantageous in that image processing can be repeated any number of times with the raw data after a shot until a desired image has been achieved, compared to other modes in which image data are non-reversibly produced by image processing made at the time of a shot. In the RAW mode recording, pixel data corresponding in number to at least the effective pixels of a solid-state image sensor are produced as raw data. More specifically, the solid-state image pickup device disclosed by the U.S. patent to Yamada mentioned earlier handles two times greater number of pixels than the CCD solid-state image pickup device of Japanese patent laid-open publication No. 2001-8104.
While semiconductor memories with its storage capacity as great as several hundred megabytes to one gigabyte are available on the market as recording media, such memories are expensive. An inexpensive semiconductor memory, however, soon becomes short of capacity when image data are recorded in the RAW mode, and therefore noticeably reduces the number of images that can be stored. Moreover, RAW mode recording extends recording time and aggravates power consumption.